An ultra low power MAC protocol is described in “Versatile low power media access for wireless sensor networks”, In Proceedings of the Second ACM SensSys, November 2004 by Polastre, J. Hill, and D. Culler.
The protocol, the B-MAC protocol, describes a random access MAC protocol that does not require nodes to be synchronised.
A source node sends, in the communication channel, a long preamble having a duration Tpreamble followed by a data packet. Periodically (every Tinterval) a possible destination node listens to the communications channel for activity. If no activity is detected the destination node keeps listening until a timeout period has expired. If activity is detected, the destination node turns on a receiver which is turned off after a data packet has been received or after a timeout period. The period Tpreamble is greater than the period Tinterval.
It will of course be understood by those skilled in the art that a preamble is a fixed predetermined sequence of bits (often 01 repeated) which is used by a correlator detector for asynchronous detection. The preamble does not, as such, convey information itself as it is fixed and predetermined.
It would be desirable to provide a MAC protocol that is more energy efficient.